View single post by Mark Rosenbaum
 Posted: 05-20-2007 06:22 pm
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Mark Rosenbaum

Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
smcmanus wrote: Needles......oops B1CM front which came with the car; B1DK rear which came with the spare carbs.  [...] Can I use the B1DK needles in the carbs which originally came on the car equipped with the B1CM needles?  

You can use either type as long as both carbs use the same type.  The B1DK gives you a somewhat richer idle which might conceivably cause emissions concerns for some cars.  Ideally both needles should show about the same amount of wear.  Also, if you care about the exact differences, I wrote an article on the topic some time ago, which IIRC can be found somewhere in the old JHPS archives.  

Are the metering "jets" the same even though the needles are different? [...] One thing is the metering jets are very slightly elevated in the venturi where on the old carb the metering jets sit down about a 16th of an inch into the body which is about correct by the book.  Can the metering jet height be adjusted? 

AFAIK, Stromberg main or metering jets come in only two bore sizes, 0.090" and 0.100".  Only the latter is used in the JH's carbs.  Ideally, both jets should sit at the same height/depth with respect to the top of the bridge into which they are pressed, though small differences can be tolerated provided they're within the range of adjustment for the mixture needles.

The jets are pressed into the body of the carb.  I've never seen that done so am not certain from which direction the jet is pressed.  It might be possible to adjust the jet position in the carb body at home, assuming one had a press or a really big vise, but there'd be some risk of ruining both jet and carb body.  Just FYI, I've attached a photo of a jet that I found on eBay awhile back.
Additionally the needles are very easy to turn in the spare carbs.  How easy should they turn?  I seems like they could easily vibrate off of the correct settings. 
Normally, the mixture needle adjusters should turn quite easily -- they're just brass-on-brass screw threads.  The anti-leak o-ring on the adjuster body seems to damp vibrations well enough that the mixture setting doesn't change much, if at all, between normal service intervals.

I think you'll be very pleased with your car's performance once you get the carbs fully dialed in.

Attachment: Main jet.jpg (Downloaded 127 times)